The invention is based on an apparatus for vibration-insulated mounting of an electric motor, in particular a blower motor.
Blower motors for heating and air conditioning blower systems that are used in vehicles, for instance, are as a rule decoupled in terms of vibration from the vehicle, in order to reduce the transmission of structure-borne sound from the motor or blower unit to the vehicle body and hence the passenger compartment of the vehicle.
Current methods of securing such motors comprise inserting the complete motor into a plastic housing or metal housing, on which a flange is provided for connection to the air conditioning system. Normally, rubber in the form of suitably shaped rubber elements is placed between the motor and the motor housing or into the flange, in order to damp sources of vibration of the air conditioning system or the vehicle body and to suppress noise that would be irritating to the driver or his passengers in the passenger compartment of the vehicle.
A primary source of vibration in d.c. motors is the commutation. The commutation occurs when the copper windings of the armature carry current during the operation of the motor. During each revolution of the armature shaft, current is carried in each direction through the existing windings of the motor. Under the influence of a permanent magnet field, the conduction of current in the windings causes a reaction that is transmitted onward in the form of a torque pulse. The number of windings, multiplied by two and taking the rpm rate into account, is the frequency of the commutation and thus the number of torque pulses transmitted by the motor per unit of time.
Accordingly, the commutation transmits torsional vibration into the heating or air conditioning blower system in accordance with the fluctuation or variations in the torque pulses. If rubber or suitable decoupling elements of rubber are placed between the flange and the motor housing, it is assured that reduced torsional vibration pulses will be transmitted into the heating and air conditioning blower system. The rubber is a mechanical filter, which prevents excessive vibration or the penetration of elevated vibration into the heating and air conditioning system and thus brings about a partial mechanical decoupling of the components.
In actual use, various possibilities exist of using rubber elements or decoupling elements of rubber between the housing flange or between the motor and the motor housing in order to damp precisely these vibration pulses.
German Patent Disclosure DE 43 34 124 A1, for instance, discloses an apparatus for receiving an electric motor that achieves an especially low-vibration and hence noise-damping effect by providing that between the inner walls of this receiving apparatus and the outer walls, facing them, of the motor housing, at least one elastic damping element is disposed, which is braced on the walls facing one another of the receiving apparatus and the motor housing.
These elastic damping elements, which in a preferred embodiment of the apparatus of DE 43 34 124 A1 are suitably shaped rubber elements, represent increased expense for assembly and material, which unnecessarily increases the costs for such an apparatus. In particular, rubber elements and rubber damping elements represent a problem for the assembly lines in industrial production, since they can be integrated into the corresponding apparatuses only by means of time-consuming manipulating processes.
From U.S. Pat. No. 4,063,060, a retaining device for an electric motor is known in which three rotationally flexible leaf-spring-like steel retaining arms are provided, which are offset from one another by the same circumferential angle, are fastened in the manner of rays between the electric motor and the receiving housing, and are each bound by one end, with the interposition of elastic buffers, to an inlet collar that is solidly connected to the receiving housing.
Because of the three-point suspension in a single plane of the electric motor in U.S. Pat. No. 4,063,060 and the low spring constant of the retaining arms in the direction of torsion, this motor executes relatively major oscillating and tilting motions, which in the elastic elements, especially the buffers, engender shear forces that rapidly cause material fatigue and damage. The service life of this known retaining device is therefore severely limited and is inadequate for use in motor vehicles, in which the elastic elements must also absorb vibration that is caused by external impacts from the roadway on the electric motor.